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Positron lifetime ( LT) and coincidence Doppler broadening ( CDB) measurements on nanopowders and ceramics of ceria- and magnesia-stabilized zirconia ( CeSZ and MgSZ, respectively) are presented. The nanopowders were prepared by the coprecipitation technique. Effects of nanopowder calcination and sintering at various temperatures were investigated. In the nanopowders, the two kinds of open-volume defects associated with grain boundaries ( GBs) could be identified via positron trapping: (i) vacancy-like misfit defects situated along GBs and (ii) larger defects at the intersections of at least three GBs (triple points). CDB measurements on CeSZ compacted nanopowders indicated a segregation of Ce ions along GBs. A few percent fractions of positrons were found to form positronium localized in pores of ≈1.8 nm diameter in compacted nanopowders. Sintering of nanopowders at 1500°C appeared to be sufficient for disappearance of pores and triple point defects. In sintered ceramics, contrary to compacted nanopowders, positrons were trapped in zirconium vacancies in grain interiors. [ABSTRACT FROM AUTHOR]

The aim of this study was to produce yttria-stabilized zirconia nanopowders from zirconium oxychloride and zirconium oxynitrate salts using a co-precipitation technique, and to investigate the influence of hydrostatic pressure on the phase transition in these powders. It is shown that synthesis conditions and calcination temperature have a strong influence on the nanopowder's agglomeration, as well as on the stability of the tetragonal phase to phase transition under pressure conditions. Doped zirconia nanopowders synthesized from oxynitrate salts are more agglomerated and more stable than the oxychloride-based powders. Increasing the role of interfacial energy in agglomerated nanopowders leads to an increase in the stability of the tetragonal phase in doped zirconia nanopowders systems obtained at low and high calcination temperatures. Formation of separated nanoparticles at middle calcination temperature leads to a decrease in the stability of the tetragonal phase to phase transition under hydrostatic pressure conditions. [ABSTRACT FROM AUTHOR]

Abstract: The difference in the magnetic properties between two lanthanum manganite nanopowders with identical phase and chemical composition is discussed in terms of the influence of nanopowder synthesis conditions on their properties. The aim of this investigation was to show the influence of precursor type and structure on the structure and properties of final La0.7Sr0.3MnO3 nanopowders obtained by precipitation technique. The forming of a complex structure of precursor materials during drying and inheritance at firing stage led to the formation of bimodal particle size distribution and magnetic properties typical of coarse powders. The correct choice of precursor material and the technological conditions of the drying and firing stage were allowed for the creation of a uniform powder structure with special magnetic properties. We showed that the magnetic properties of nanopowders were not always determined by chemical or phase composition and mean particle size of synthesized powders. The difference in precipitation process can lead to unpredictable and catastrophic results, and masked the effect of nanoparticles on the magnetic properties of the material. [Copyright &y& Elsevier]